When the clutch pedal of a hydraulically actuated, vehicular clutch is depressed by the driver, a master cylinder provides fluid, under pressure, to a remote slave cylinder, and the piston shaft of the slave cylinder releases the clutch to interrupt the drive train between the engine and the wheels of the vehicle. This interruption occurs as a result of releasing the engaging pressure between the driving and driven members of the clutch assembly.
The driving members of the clutch assembly normally consist of two flat, smoothly finished surfaces. One of the two finished surfaces on the driving members is generally the rear face of the flywheel which is affixed to, and rotates with, the crankshaft of the engine. The other of the two finished surfaces is normally the opposed surface of a pressure plate. The pressure plate is usually mounted within a cover assembly that is secured to the flywheel.
The driven member of the clutch assembly is a clutch disk which is interposed between the opposed driving members. The clutch disk is, in turn, operatively secured to the transmission input shaft by which power is provided to the transmission. To accommodate wear, and to assure that the clutch plate may be properly engaged by the driving members, the clutch disk employs a splined hub which permits the clutch plate to slide axially along corresponding splines on the input shaft.
The driving and driven members are normally maintained in contact by the biasing pressure of a spring means--such as a Belleville spring which is included within the cover assembly--to assure that the frictional contact between the driving and driven members will cause the driven member to rotate with the driving members. A clutch release system is employed to overcome the biasing action of the spring means and thereby allow the driving members to rotate without imparting rotation to the driven member.
The clutch release system may be either mechanical or hydraulic, and the present invention relates to improvements with respect to the hydraulic clutch release systems.
It is generally known that the sudden applications of force caused by the initiation of each power stroke in a cylinder--i.e., by the "firing" of each cylinder--in a vehicle engine are transmitted from the engine, through the clutch and clutch release mechanism, to the foot pedal of the clutch and hence, to the foot of the vehicle operator. A standard, V-6 engine will, for example, produce three power strokes for every revolution of the crankshaft. V-6 engines ordinarily operate in the range of from about 2000 to about 5500 revolutions per minute (RPM), and the frequencies of the power strokes which provide the stated revolutions, when felt as vibrations in the foot pedal of the clutch release system, are undesirable.
Similarly, acceptable manufacturing irregularities in the flywheel which result in axial displacement to components within the clutch mechanism induce vibrations at frequencies that are mathematically dependent upon the RPM of the engine, and those vibrations are also fed, as pulsations, through the hydraulic clutch release system to be felt as vibrations in the foot pedal of the clutch release system.
Historic clutch mechanisms generally allowed sufficient slippage, or were provided with surge-suppressing, spring mechanisms that tended to dampen most torque induced vibrations and thereby reduced the transmission of undesirable pulsations through the hydraulic system of the clutch release system. However, with advancements in clutch technology, the internal friction within the clutch mechanism has reduced slippage. While this has beneficially promoted more efficient clutch operation and reduced wear, it has adversely permitted more vibrations to be transmitted to the foot pedal of the clutch.
One prior art approach utilized in an attempt to reduce the vibrations imposed upon the foot pedal of the clutch has been to supply an accumulator for use in association with hydraulic clutch release systems. Accumulators dissipate fluid pulsations by transferring the oscillatory motion into heat energy, normally through the compression and expansion of a fluid, be it a liquid or a gas.
U.S. Pat. No. 4,301,908 issued to Fukuda et al., Nov. 24, 1981, discloses an accumulator-type vibration reducing device. The device disclosed in said patent employs a piston slidably received within an oil chamber. The accumulator piston is biased by a resilient rubber, or coil spring, member so it will reciprocate in response to pulsations transmitted by the hydraulic fluid. The accumulator is interposed within the hydraulic clutch control mechanism between the foot pedal and the clutch mechanism in order to intercept and dampen hydraulic pulsations before they reach the foot pedal as vibrations. This device utilizes a number of moving parts which are, therefore, subject to wear. It is appreciated by those skilled in the art that an accumulator, by its nature and function, is subject to dynamic forces that are constantly changing in both magnitude and direction. This also induces increased wear and reduced performance. Moreover, tests have shown that while such an arrangement may be quite effective for pulsations across a wide range of frequencies, it is not necessarily effective for pulsations within all ranges of the frequencies that are typically encountered when operating a V-6 engine within the normal range of RPM previously mentioned herein.